The significance of block copolymers is evident in light of the wide array of properties they possess. These properties are due to the arrangement of different polymers in alternating sequence. Block copolymers are exceptionally interesting because they can “microphase separate” to form periodic nanostructures. Block copolymers can also self-assemble, similar to small surfactant molecules, to form micelles. Due to these inherent properties, block copolymers can be used in a wide range of applications.
Self assembly of amphiphilic block copolymers in aqueous solution has received attention in the past few decades due to their potential applications in nanotechnology and nanobiotechnology (Allen et. al. [1999] Colloids and Surfaces B. 16:3-27, Kraemer et. al. [2002] Angew. Chem. Int. Ed. 22: 41). Most developments of aqueous-based formulations have focused on drug delivery systems.
There are two principal ways for preparing amphiphilic block copolymer micelles in aqueous solution: the direct dissolution method and the indirect method (Allen et. al. [1999] Colloids and Surfaces B. 16:3-27). Polymers that are poorly soluble in water require the indirect method i.e. dialysis or solvent evaporation. Dialysis is a slow process and is limited to low volumes. Solvent evaporation creates low-volatile organic compound (VOC) problems and may require expensive recovery processes. Also, the above mentioned indirect method involves transferring amphiphilic block copolymers from water miscible solvents such as dimethylformamide, tetrahydrofuran or dimethylacetamide to aqueous solution.
Related work on phase transfer process was employed for transferring inorganic nanoparticles from organic phase to aqueous phase using a small molecule 4-dimethylaminopyridine (DMAP) as the phase transfer agent (Caruso et. al. [2006] US Patent Publication No. 2006/0084705 A1). Their process is limited to the organic phase having lower density than the aqueous phase and also requires high concentrations of the phase transfer agent. However, until this invention, the phase transfer process using a phase transfer agent to transfer amphiphilic block copolymer from organic to aqueous phase to obtain micelles and micellar aggregates has not been developed.